This invention relates to biodegradable resin which has been recently spotlighted in place of synthetic resin, and more particularly to a biodegradable resin foam obtained by foaming the biodegradable resin and a method and an apparatus for producing the same.
In general, synthetic resin has been applied to a variety of industrial fields because of exhibiting satisfactory mass productivity, moldability and durability. In particularly, a synthetic resin foam is light-weight and exhibits increased cushioning properties, to thereby be widely used in various forms such as a protective casing for a fragile article such as a glass product, a cushioning material for packing, a tableware, a heat insulation material, a sound insulation material and the like. However, this causes the amount of disposal of such synthetic resin products to be extensively increased, leading to various serious problems.
More particularly, incineration of synthetic resin causes a large amount of harmful gas to be produced, leading to atmospheric pollution. Disposal of synthetic resin other than the incineration causes environmental pollution because it has resistance to oxidation and resistance to decomposition by light and ozone. Also, synthetic resin is extensively increased in intermolecular bond, so that the incineration causes generation of much heat, leading to damage to an incineration furnace and therefore a decrease in lifetime of the furnace.
In view of the foregoing, much attention has been recently directed to biodegradable resin and a great effort has been made to develop biodegradable resin.
As a result, processing of biodegradable resin into a film material is now in the course of being put into practice. Also, development of foaming of biodegradable resin would lead to spread of applications thereof, to thereby permit advantages of biodegradable resin to be more widely exhibited. Techniques of foaming synthetic resin which have been carried out in the art include a method of producing foamed beads including the steps of charging styrene beads in a forming mold and adding water vapor thereto, followed by a decrease in pressure, a method of foaming synthetic resin by charging an extruder with, for example, styrene resin together with a foaming agent such as an organic solvent or the like to foam the resin due to a pressure reducing action occurring when the resin is extruded, and the like.
However, such conventional chemical foaming techniques for foaming synthetic resin as described above fail to satisfactorily foam biodegradable resin due to a relationship between a softening point or melting point of the resin and a foaming temperature of a foaming agent and the like. Thus, there are known many problems which are encountered with techniques of foaming biodegradable resin to a high degree and forming the foamed resin.
A first problem occurs when a biodegradable resin foam is to be produced by means of, for example, an injection molding machine used for production of a conventional synthetic resin foam. More particularly, when biodegradable resin fluidized due to heating and pressurization in a cylinder is extruded through a nozzle of the cylinder into a forming mold, to thereby be decreased in pressure, moisture in the resin is vaporized, leading to expansion. The moisture vaporized is then decreased in temperature, resulting in suspending in the form of steam in the mold or being condensed on an inner surface of the mold or an outer surface of a molded product. Biodegradable resin generally exhibits increased hygroscopicity, resulting in being readily softened and swollen when it is contacted wit moisture. In particular, a film of each of foamed cells on an outer portion of a molded or formed product is excessively decreased in thickness, so that it is readily softened when it absorbs condensed water. This results in the foamed cells being readily collapsed. Such collapse of the cells is also caused due to re-adhesion of moisture evaporated from the resin to the cells. The collapse causes portions of the formed product at which the cells are collapsed to be shrunk, leading to deformation of the formed product. When the formed product thus deformed is solidified, it is caused to be in a solid form substantially free of any foamed cell. Thus, the formed product thus obtained by injection molding fails to exhibit desired cushioning performance.
A second problem is that the conventional chemical foaming techniques fail to provide a foamed product having a desired configuration and exhibiting a satisfactory cushioning function. More particularly, foaming of biodegradable resin is started upon release from a pressurized state, however, it is highly hard to reach the depths of a forming mold because of exhibiting increased viscosity when it is fluidized by heating. Therefore, foaming of biodegradable resin partially occurs before the resin extruded from the cylinder reaches the depths of the forming mold, resulting in a part of the resin which is to be foamed in the depths of the mold carrying out foaming in the middle of the mold, so that any cavity and/or void are formed in the foamed resin. Such a problem tends to occur in a forming mold of a complicated configuration, Thus, the so-formed biodegradable resin foam is pressedly forced by biodegradable resin subsequently extruded, so that the portion of the resin which carried out foaming on the way to the depths of the mold is crushed by the subsequently extruded resin. Thus, the prior art fails to form the foamed resin into a desired configuration. Also, the foamed resin fails to exhibit a satisfactory cushioning performance.
A third problem occurs due to releasing of biodegradable resin fluidized by heating and pressurizing from a heated and pressurized environment. Releasing of the resin fluidized causes moisture contained in the resin to be vaporized and expanded, resulting in foaming of the resin, to thereby provide cells, during which the cells-are decreased in temperature to a level of about 100xc2x0 C. due to vaporization of the moisture. This causes the cells to be somewhat shrunk and then solidified while being kept shrunk. Also, the cells are somewhat shrunk by water vapor surrounding the cells. Such cells are integrated together to form a foam. Thus, cavities and/or voids occur in the foam solidified, so that boundaries between the cells are discontinuous, to thereby cause the foam to be unsuitable for use for a cushioning material.
A fourth problem encountered with the conventional chemical foaming techniques is caused during formation of an pressure reduced atmosphere. More particularly, when a heated and pressurized atmosphere in which biodegradable resin is placed is to be changed into a pressure reduced atmosphere, an evacuation or vacuum pump is generally used. Unfortunately, formation of such a pressure reduced atmosphere requires a considerable period of time, so that a pressure reducing action due to the change is rendered slow or inactive. Also, this causes moisture to re-adhere to cells while it is not fully exhausted, leading to softening of the cells, followed by collapse of the cells, resulting in the resultant resin foam being deteriorated in properties or quality. In order to prevent such re-adhesion of moisture to the cells, it would be considered that formation of the pressure reduced atmosphere is carried out using a large-sized vacuum pump or the like, resulting in time required for evacuation being reduced. However, this causes a significant increase in manufacturing cost of the foam.
Further, injection of biodegradable resin from a nozzle of a cylinder of an injection molding machine into a forming mold arranged in a closed atmosphere causes injection resistance to be increased. In order to avoid the problem, it is required to arrange a large-sized injection molding machine. Unfortunately, this leads to an increase in cost of equipment and therefore manufacturing cost. In particular, in order to form a foam with high configuration accuracy, it is required to permit biodegradable resin to be spread throughout the forming mold. This is advantageously-accomplished by keeping an atmosphere in the forming mold pressurized during injection molding. However, this causes injection resistance to be further increased, resulting in the above-described disadvantage being rendered amplified.
The present invention has been made in view of the foregoing disadvantages of the prior art.
Accordingly, it is an object of the present invention to provide a method for producing a biodegradable resin foam which is capable of accomplishing foaming of biodegradable resin while minimizing or substantially preventing shrinkage of formed biodegradable resin due to re-adhesion of moisture thereto, to thereby provide a uniform biodegradable resin foam.
It is another object of the present invention to provide a method for producing a biodegradable resin foam which is capable of uniformly foaming biodegradable resin.
It is a further object of the present invention to provide a method for producing a biodegradable resin foam which is capable of minimizing or substantially preventing collapse of cells of foamed biodegradable resin to provide a biodegradable resin foam of a desired configuration and uniform quality.
It is still another object of the present invention to provide a method for producing a biodegradable resin foam which is capable of providing a water-repellent biodegradable resin foam.
It is yet another object of the present invention to provide a method for producing a biodegradable resin foam which is capable of providing a biodegradable resin foam free of any discontinuous boundary between cells even when any cavity and/or void occurs in biodegradable resin foamed.
It is even another object of the present invention to provide a biodegradable resin foam which is substantially free of any discontinuous boundary between cells even when any cavity and/or void occurs in biodegradable resin foamed.
It is a still further object of the present invention to provide an apparatus for producing a biodegradable resin foam which is capable of preventing an increase in cost of equipment and accomplishing rapid pressure reduction and evacuation of an atmosphere in a forming mold at an appropriate timing, to thereby provide a biodegradable resin foam of improved quality.
It is a yet further object of the present invention to provide an apparatus for producing a biodegradable resin foam which is capable of preventing an increase in cost of equipment and facilitating injection of biodegradable resin into a forming mold while keeping injection resistance at a minimum level, to thereby increase configuration accuracy of a biodegradable resin foam.
In accordance with one aspect of the present invention, a biodegradable resin foam is provided which is made of biodegradable resin by expansion force due to vaporization of moisture caused by rapidly releasing fluidized biodegradable resin which is in a heated and pressurized environment and in which the moisture is trapped. The biodegradable resin may comprise a combination of a first biodegradable resin ingredient having a melting point of 100xc2x0 C. or more or a main biodegradable resin ingredient and a second biodegradable resin ingredient having a melting point of 100xc2x0 C. or less or a low-melting biodegradable resin ingredient.
In a preferred embodiment of the present invention, the second biodegradable resin ingredient may be selected from the group consisting of polycaprolactone and a material containing polycaprolactone.
In a preferred embodiment of the present invention, the biodegradable resin may have a substance selected from the group consisting of polyhydric alcohols and derivatives thereof added thereto.
Thus, in the foam of the present invention, the second biodegradable resin ingredient is kept from being immediately solidified, to thereby function as an adhesive with respect to the first biodegradable resin ingredient. Therefore, even when any cavity and/or void are unfortunately formed in the foamed biodegradable resin, cells of the foamed resin are permitted to adhere to each other through the second resin ingredient, resulting in the foam being provided with satisfactory quality.
When the second biodegradable resin ingredient is selected from the group consisting of polycaprolactone and a material containing polycaprolactone, the function of the second biodegradable resin ingredient as an adhesive is substantially enhanced. Also, when the biodegradable resin has polyhydric alcohols and derivatives thereof added thereto, moisture in the resin is increased in boiling point, resulting in functioning also as a plasticizer, so that cells of the foamed biodegradable resin are rendered dense and uniform.
In accordance with another aspect of the present invention, a method for producing a biodegradable resin foam is provided. The method comprises the steps of charging a biodegradable resin starting material containing biodegradable resin in a cylinder formed at a front portion thereof with a narrowed opening, raising a temperature of the biodegradable resin to render the biodegradable resin fluidized while forcibly transferring the biodegradable resin starting material toward the narrowed opening in the cylinder, extruding the fluidized biodegradable resin from the cylinder into an air-permeable forming mold arranged in front of the cylinder to rapidly release the biodegradable resin from a heated and pressurized environment in the cylinder to foam the biodegradable resin, and forming the foamed biodegradable resin into a shape depending on a configuration of the forming mold. Thus, moisture contained in the resin is increased in boiling point under pressure, resulting in being in the form of liquid in the cylinder, so that releasing of the resin from the heated and pressurized environment in the cylinder causes the moisture to be instantaneously vaporized, leading to foaming of the resin. The resultant water vapor is outwardly discharged through the air-permeable forming mold, to thereby be prevented from re-adhering to the formed foam.
In a preferred embodiment of the present invention, an atmosphere in which the forming mold is placed is kept decreased in pressure or ventilated since a stage before starting of extrusion of the fluidized biodegradable resin into the forming mold or since starting of the extrusion. Such construction prevents moisture from remaining in the form of steam in the forming mold or being condensed on a surface of the resin foam due to a decrease in temperature after vaporization and expansion of the moisture, resulting in the form being provided with satisfactory uniformity.
In a preferred embodiment of the present invention, the step of extruding the fluidized biodegradable resin into the mold is carried out while placing a nozzle arranged with respect to the narrowed opening in the depths of the forming mold at the time of starting of the nozzle and retracting the nozzle relative to the forming mold during extrusion of the biodegradable resin. This permits the biodegradable resin to be charged in the forming mold in order from the side of the depths of the mold, resulting in a difference between a timing at which the resin is spread throughout the forming mold and a timing of foaming of the resin being minimized or substantially eliminated, to thereby substantially prevent cells of the foamed biodegradable resin from being collapsed.
In a preferred embodiment of the present invention, the step of extruding the fluidized biodegradable resin into the forming mold is carried out while keeping an atmosphere in the forming mold pressurized during the extrusion and rapidly reducing a pressure of the atmosphere in the forming mold after completion of the extrusion. This permits the biodegradable resin to be foamed while being spread throughout the forming mold, so that the resin foam obtained is formed into a desired configuration.
In a preferred embodiment of the present invention, the step of extruding the fluidized biodegradable resin into the forming mold is carried out by injecting the biodegradable resin into the forming mold while keeping the resin atomized. This permits not only the resin to be spread throughout the forming mold but the atomized resin to be effectively foamed, followed by integration of cells of the foamed resin without being collapsed, to thereby provide the-resin foam with increased uniformity.
In a preferred embodiment of the present invention, the biodegradable resin starting material may comprise moisture and the biodegradable resin. Alternatively, it may comprise the biodegradable resin and a hygroscopic fine-particle material having moisture absorbed therein and added to the biodegradable resin. Also, the biodegradable resin starting material may comprise moisture, the biodegradable resin and a water repellent material. The starting material of such composition ensures desired foaming of the resin and permits it to be finely and uniformly foamed.
Also, the water repellent material may comprise a material which is not fully evaporated when the resin fluidized is released from the heated and pressurized environment. The material may include a natural fatty acid polymer. Use of the polymer as the water repellent material permits it to cover cells of the foamed resin to provide it with water repellent properties, to thereby prevent the cells from being collapsed due to contact with water.
In a preferred embodiment of the present invention, the step of forming the foamed biodegradable resin into a shape depending on a configuration of the forming mold may be carried out by forming the whole biodegradable resin into an integrated configuration. This permits the resin foam to be formed into a relative large volume or any desired configuration.
In a preferred embodiment of the present invention, the biodegradable resin comprises a first biodegradable resin ingredient having a melting point of 100xc2x0 C. or more and a second biodegradable resin ingredient having a melting point of 100xc2x0 C. or less.
In a preferred embodiment of the present invention, the second biodegradable resin ingredient is selected from the group consisting of polycaprolactone and a material containing it.
In a preferred embodiment of the present invention, the biodegradable resin has a substance selected from the group consisting of polyhydric alcohols and derivatives thereof added thereto.
In accordance with a further aspect of the present invention, an apparatus for producing a biodegradable resin foam is provided. The apparatus comprises a pressure adjusting chamber constructed in a manner to be capable of being opened and closed hermetically, an air-permeable forming mold arranged in the pressure adjusting chamber, a pressure reducing tank connected to the pressure adjusting chamber to rapidly reduce a pressure in the pressure adjusting chamber, and an injection machine for injecting, into the forming mold, fluidized biodegradable resin placed in a heated and pressurized environment and having moisture trapped therein. Thus, the apparatus permits the pressure reducing tank to communicate with the pressure adjusting chamber after injection of the resin into the forming mold, so that water vapor produced in the forming mold may be effectively outwardly discharged, to thereby eliminate retention of moisture in the forming mold. Thus, the biodegradable resin foam product obtained is provided with a desired configuration and uniform quality.
In a preferred embodiment of the present invention, the pressure adjusting chamber has an evacuation valve connected thereto. Thus, when the pressure adjusting chamber is rendered open to an ambient atmosphere in the course of injection of the rein into the forming mold, resistance to the injection is reduced because the forming mold is air-permeable, so that the injection may be facilitated. Therefore, the injection machine is prevented from being large-sized.
In a preferred embodiment of the present invention, the pressure adjusting chamber has a compressor connected thereto. This permits injection of the resin into the forming mold to be carried out while keeping moisture positively trapped in the resin because actuation of the compressor pressurizes the pressure adjusting chamber. Then, operation of the evacuation valve results in the pressure adjusting chamber being released from pressurization, leading to a decrease in injection resistance, so that the resin may be spread throughout the forming mold.
In a preferred embodiment of the present invention, the pressure adjusting chamber has a pressurizing tank connected thereto. This permits the pressure adjusting chamber to be rapidly pressurized at an appropriate timing when the resin is to be injected into the forming mold.
Also, in accordance with this aspect of the present invention, an apparatus for producing a biodegradable resin foam is provided. The apparatus comprises a pressure adjusting chamber constructed in a manner to be capable of being opened and closed hermetically, an air-permeable forming mold arranged in the pressure adjusting chamber, a pressure reducing tank connected through a pressure reducing valve to the pressure adjusting chamber to rapidly reduce a pressure in the pressure adjusting chamber, an evacuation valve connected to the pressure adjusting chamber, a compressor connected to the pressure adjusting chamber, a valve controller for controlling operation of each of the valves, and an injection machine for injecting, into the forming mold, fluidized biodegradable resin placed in a heated and pressurized environment and having moisture trapped therein. The valve controller functions to initiate actuation of the compressor before or at the time when injection of the biodegradable resin into the forming mold by the injection machine is started, carry out termination of actuation of the compressor and opening of the evacuation valve in the course of the injection, and carry out closing of the evacuation valve and opening of the pressure reducing valve after the injection. Thus, the pressure adjusting chamber may be controlled to pressurization, evacuation or pressure reduction in association with a timing of injection of the resin into the forming mold.
Further, in accordance with this aspect of the present invention, an apparatus for producing a biodegradable resin foam is provided. The apparatus comprises a pressure adjusting chamber constructed in a manner to be capable of being opened and closed hermetically, an air-permeable forming mold arranged in the pressure adjusting chamber, a pressure reducing tank connected through a pressure reducing valve to the pressure adjusting chamber to rapidly reduce a pressure in the pressure adjusting chamber, an evacuation valve connected to the pressure adjusting chamber, a pressurizing tank connected through a pressurizing valve to the pressure adjusting chamber, a valve controller for controlling operation of each of the valves, and an injection machine for injecting, into the forming molds fluidized biodegradable resin placed in a heated and pressurized environment and having moisture trapped therein. The valve controller functions to open the pressurizing valve before or at the time when injection of the biodegradable resin into the forming mold by the injection machine is started, carry out closing of the pressurizing valve and opening of the evacuation valve in the course of the injection, and carry out closing of the evacuation valve and opening of the pressure reducing valve after the injection. Thus, the pressure adjusting chamber is controlled to pressurization, evacuation or pressure reduction in association with a timing of the injection.
In addition, in accordance with this aspect of the present invention, an apparatus for producing a biodegradable resin foam is provided. The apparatus comprises a pressure adjusting chamber constructed in a manner to be capable of being opened and closed hermetically, an air-permeable forming mold arranged in the pressure adjusting chamber, a pressure reducing tank connected through a pressure reducing valve to the pressure adjusting chamber to rapidly reduce a pressure in the pressure adjusting chamber, an evacuation valve connected to the pressure adjusting chamber, a valve controller for controlling operation of each of the valves, and an injection machine for injecting, into the forming mold, fluidized biodegradable resin placed in a heated and pressurized environment and having moisture trapped therein. The valve controller functions to open the evacuation valve in the course of injection of the biodegradable resin into the forming mold by the injection machine and carry out closing of the evacuation valve and opening of the pressure reducing valve after the injection. Thus, the pressure adjusting chamber is controlled to evacuation or pressure reduction in association with a timing of the injection.
Furthermore, in accordance with this aspect of the present invention, an apparatus for producing a biodegradable resin foam is provided. The apparatus comprises a pressure adjusting chamber constructed in a manner to be capable of being opened and closed hermetically, an air-permeable forming mold arranged in the pressure adjusting chamber, a pressure reducing tank connected through a pressure reducing valve to the pressure adjusting chamber to rapidly reduce a pressure in the pressure adjusting chamber, a pressurizing tank connected through a pressurizing valve to the pressure adjusting chamber, a valve controller for controlling operation of each of said valves, and an injection machine for injecting, into the forming mold, fluidized biodegradable resin placed in a heated and pressurized environment and having moisture trapped therein. The valve controller functions to open the pressurizing valve before or at the time when injection of the biodegradable resin into the forming mold by the injection machine is started and carry out closing of the pressurizing valve and opening of the evacuation valve after the injection. This permits the pressure adjusting chamber to be controlled to pressurization or pressure reduction in association with a timing of the injection.
In a preferred embodiment of the present invention, the injection machine includes a cylinder having a narrowed opening formed at a front portion thereof, a forcible transfer mechanism for forcibly transferring a biodegradable resin starting material containing biodegradable resin and charged in the cylinder and raising a temperature of the biodegradable resin, to thereby fluidize it and extruding the fluidized biodegradable resin through the narrowed opening into a forming mold, and an access mechanism for reciprocating the narrowed opening and forming mold relative to each other and retracting the narrowed opening relative to the forming mold during injection of the fluidized biodegradable resin through the narrowed opening into the forming mold.